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Abstract:

A method for communicating DM-RS symbols to support MIMO transmissions
having five or more layers of spatial multiplexing. A first subframe is
communicated carrying two leading symbols of a first length-4 OCC
sequence and two leading symbols of a second length-4 OCC sequence, and a
second subframe is communicated carrying two trailing symbols of the
first length-4 OCC and two trailing symbols of the second length-4 OCC
sequence. Optionally four length-2 OCCs can be carried in a similar
manner or, alternatively, in different frequency bands or resource block
pairs of a common subframe.

Claims:

1. A method of communicating reference signal symbols, the method
comprising: communicating a first subframe in a channel, the first
subframe carrying a first set of symbols of a first spreading code
sequence and a first set of symbols of a second spreading code sequence;
and communicating a second subframe in a channel, the second subframe
carrying a second set of symbols of the first spreading code and a second
set of symbols of the second spreading code sequence.

2. The method of claim 1, wherein channel state information of the
channel is obtained by performing channel estimation on all symbols of
the first spreading code sequence and all symbols of the second spreading
code sequence.

3. The method of claim 2, wherein both the second set of symbols of the
first spreading code sequence and the second set of symbols of the second
spreading code sequence are excluded from the first subframe, and wherein
both the first set of symbols of the first spreading code sequence and
the first set of symbols of the second spreading code sequence are
excluded from the second subframe.

4. An apparatus for communicating reference signal symbols, the apparatus
comprising: a processor; and a computer readable storage medium storing
programming for execution by the processor, the programming including
instructions to: communicate a first subframe in a channel, the first
subframe carrying a first set of symbols of a first spreading code
sequence and a first set of symbols of a second spreading code sequence;
and communicate a second subframe in a channel, the second subframe
carrying a second set of symbols of the first spreading code and a second
set of symbols of the second spreading code sequence.

5. The apparatus of claim 4, wherein channel state information of the
channel is obtained by performing channel estimation on all symbols of
the first spreading code sequence and all symbols of the second spreading
code sequence.

6. The apparatus of claim 5, wherein both the second set of symbols of
the first spreading code sequence and the second set of symbols of the
second spreading code sequence are excluded from the first subframe, and
wherein both the first set of symbols of the first spreading code
sequence and the first set of symbols of the second spreading code
sequence are excluded from the second subframe.

7. A method of communicating reference signal symbols, the method
comprising: communicating a first subframe in a downlink channel, the
first subframe carrying a first symbol and a second symbol of a first
length-4 orthogonal cover code (OCC) sequence and a first symbol and a
second symbol of a second length-4 OCC sequence; and communicating a
second subframe in the downlink channel, the second subframe carrying a
third symbol and a fourth symbol of the first length-4 OCC and a third
symbol and a fourth symbol of the second length-4 OCC sequence.

8. The method of claim 7, wherein channel estimation is performed on all
four symbols of the first length-4 OCC sequence and all four symbols of
the second length-4 OCC sequence to support multiple-input and
multiple-output (MIMO) transmissions in the downlink channel.

9. The method of claim 8, wherein communicating all four symbols of the
first length-4 OCC sequence and all four symbols of the second length-4
OCC sequence supports spatial multiplexing that utilizes five or more
antenna ports.

10. The method of claim 7, wherein communicating the first subframe
includes failing to successfully transmit the last symbol of the first
subframe, the failure to successfully transmit the last symbol of the
first subframe being attributable to a symbol-loss of the first subframe.

11. The method of claim 10, wherein the first subframe and the second
subframe each comprise fourteen time-slots.

12. The method of claim 10, wherein the first subframe and the second
subframe each comprise twelve time-slots.

13. The method of claim 7, wherein both the third symbol and the fourth
symbol of the first length-4 OCC sequence are omitted from the first
subframe, and wherein both the first symbol and the second symbol of the
first length-4 OCC sequence are omitted from the second subframe

14. The method of claim 7, wherein channel estimation on the first
length-4 OCC sequence supports a first set of four antenna ports, and
wherein channel estimation on the second length-4 OCC sequence supports a
second set of four antenna ports, the second set of four antenna ports
including different antenna ports than the first set of four antenna
ports.

15. A method of communicating reference signal symbols, the method
comprising: communicating a first subframe in a downlink channel, the
first subframe comprising: a first resource block pair (RBP) carrying a
first symbol and a second symbol of a first length-4 orthogonal cover
code (OCC) sequence; and a second RBP carrying a first symbol and a
second symbol of a second length-4 OCC sequence, the second RBP and the
first RBP spanning different frequency bands of the downlink channel.

16. The method of claim 15, wherein the second subframe comprises: a
third RBP carrying a third symbol and a fourth symbol of the first
length-4 OCC sequence, wherein the third RBP and the first RBP span
identical frequency bands of the downlink channel; and a fourth RBP
carrying a third symbol and a fourth symbol of the second length-4 OCC
sequence, wherein the fourth RBP and the second RBP span identical
frequency bands of the downlink channel.

17. An apparatus for communicating reference signal symbols, the
apparatus comprising: a processor; and a computer readable storage medium
storing programming for execution by the processor, the programming
including instructions to: communicate a first subframe in a downlink
channel, the first subframe carrying a first symbol and a second symbol
of a first length-4 orthogonal cover code (OCC) sequence; and communicate
a second subframe in the downlink channel, the second subframe carrying a
third symbol and a fourth symbol of the first length-4 OCC.

18. The apparatus of claim 17, wherein communicating all four symbols of
the first length-4 OCC sequence supports spatial multiplexing that
utilizes five or more antenna ports.

19. The apparatus of claim 17, wherein the first subframe and the second
subframe comprise fourteen timeslots each, and wherein communicating the
first subframe includes failing to successfully transmit the last
timeslot of the first subframe, the failure to successfully transmit the
last symbol of the first subframe being attributable to a symbol-loss of
the first subframe.

20. The apparatus of claim 17, wherein both the third symbol and the
fourth symbol of the first length-4 OCC sequence are omitted from the
first subframe, and wherein the first symbol and the second symbol of the
first length-4 OCC sequence are omitted from the second subframe.

21. The apparatus of claim 17, wherein the first subframe further
comprises a first symbol and a second symbol of a second length-4
orthogonal cover code (OCC) sequence, wherein the second subframe further
comprises a third symbol and a fourth symbol of the second length-4 OCC.

22. A method of communicating reference signal symbols, the method
comprising: communicating a first subframe in a downlink channel, the
first subframe carrying a first length-2 orthogonal cover code (OCC)
sequence and a second length-2 OCC sequence; and communicating a second
subframe in the downlink channel, the second subframe carrying a third
length-2 OCC sequence and fourth length-2 OCC sequence.

23. The method of claim 22, wherein the first subframe comprises: a first
resource block pair (RBP) carrying the first length-2 OCC sequence; and a
second RBP carrying the second length-2 OCC sequence, the second RBP and
the first RBP spanning different frequency bands of the downlink channel.

24. An apparatus for communicating reference signal symbols, the
apparatus comprising: a processor; and a computer readable storage medium
storing programming for execution by the processor, the programming
including instructions to: communicate a first subframe in a downlink
channel, the first subframe carrying a first length-2 orthogonal cover
code (OCC) sequence and a second length-2 OCC sequence; and communicate a
second subframe in the downlink channel, the second subframe carrying a
third length-2 OCC sequence and fourth length-2 OCC sequence.

25. A method of communicating reference signal symbols, the method
comprising: communicating a first subframe in a downlink channel, the
first subframe comprising: a first resource block pair (RBP) carrying a
first length-2 orthogonal cover code (OCC) sequence and a second length-2
OCC sequence, wherein both the first length-2 OCC sequence and the second
length-2 OCC sequence correspond to a first set of four antenna ports;
and a second RBP carrying a third length-2 OCC sequence and a fourth
length-2 OCC sequence, wherein both the third length-2 OCC sequence and
the fourth length-2 OCC sequence correspond to a second set of four
antenna ports that is different from the first set of antenna ports,
wherein channel estimation is performed on the first length-2 OCC
sequence, the second length-2 OCC sequence, the third length-2 OCC
sequence, and the fourth length-2 OCC sequence to support five or more
antenna ports.

26. The method of claim 25, wherein the first RBP and the second RBP span
different frequency bands of the downlink channel.

Description:

[0001] This application claims the benefit of U.S. Provisional Application
No. 61/505,922, filed by Sartori et al. on Jul. 8, 2011, entitled "UE
Specific RS Configurations for a Relay Backhaul Link," which is
incorporated by reference herein as if reproduced in its entirety.

TECHNICAL FIELD

[0002] The present invention relates generally to digital communications,
and more particularly to a system and method for signaling reference
signals, or measuring channel state information using reference signals
in a communications system.

BACKGROUND

[0003] Modern wireless systems often use multiple-input and
multiple-output (MIMO) transmission techniques to achieve higher data
rates. MIMO transmission generally refers to the utilization of multiple
antennas at the transmitter and/or receiver, and includes a variety of
diverse techniques including spatial multiplexing, diversity coding,
pre-coding, etc. In particular, using spatial multiplexing by sending
multiple spatial streams for a single user is quite useful in
high-interference networks because it splits a relatively high data-rate
signal into multiple lower data-rate streams, which helps lower the
bit-error-rate (BER) of the communication channel. Notably, each of the
lower data-rate streams is transmitted by a different transmission
antenna port in a common frequency channel, with each individual stream
being recognized upon reception by its unique spatial signature (e.g.,
transmit and/or receive weights). Hence, spatial multiplexing essentially
enables the transmitter to communicate parallel streams (e.g., spatial
multiplexed layers) of information over the same frequency band.

[0004] The maximum number of spatial multiplexing streams/layers (Ns)
is limited by the lesser of the number of antennas at the transmitter
(Nt) or the number of antennas at the receiver (Nr), e.g.,
Ns=min(Nt, Nr). Generally speaking, additional layers of
spatial multiplexing increase spectral efficiency in the channel, thereby
allowing for greater throughput, simultaneously supporting more
transmitting users, etc. For instance, a network supporting eight layers
of spatial multiplexing (e.g., Ns=8) may generally outperform a
network supporting only four layers of spatial multiplexing (e.g.,
Ns=4). As such, modern communications standards are trending towards
the utilization of more and more layers of spatial multiplexing (i.e.,
the use of more antenna ports). For instance, 3rd Generation Partnership
Project (3GPP) long term evolution (LTE) release 10 (rel-10) specifies
supporting up to eight layers of spatial multiplexing (e.g., 8 antennas
at the transmitter and receiver).

[0005] To utilize spatial multiplexing effectively, the transmitter must
generally have some knowledge of the communications channel, which (in
the context of LTE) is generally referred to as channel state information
(CSI). Specifically, CSI is obtained when a user equipment (UE) or relay
node (RN) performs channel estimation on a reference signal that is
propagated through the downlink channel, e.g., the physical downlink
shared channel (PDSCH) or physical downlink control channel (PDCCH). The
CSI may then be feedback to the base station directly (e.g., via an
uplink control channel), or indirectly (e.g., by sending an indicator
related to the CSI using channel reciprocity for a Time Division
Duplexing (TDD)). In 3GPP LTE rel-10, the reference signal may be a
dedicated/de-modulation reference signal (DM-RS) capable of supporting up
to eight layers.

SUMMARY

[0006] Example embodiments provide a system and method for carrying DM-RS
symbols in a communications system.

[0007] In an embodiment, a method of communicating reference signal
symbols is provided. In this example, the method includes communicating,
in a channel, a first subframe carrying a first set of symbols of a first
spreading code sequence and a first set of symbols of a second spreading
code sequence. The method further includes communicating, in the channel,
a second subframe in a channel carrying a second set of symbols of the
first spreading code and a second set of symbols of the second spreading
code sequence.

[0008] In another embodiment, a method of communicating reference signal
symbols is provided. In this example, the method includes communicating a
first subframe carrying a first and second symbol of a first length-4 OCC
sequence and a first and second symbol of a second length-4 OCC sequence.
The method further includes communicating a second subframe carrying a
third and fourth symbol of the first length-4 OCC and a third and fourth
symbol of the second length-4 OCC sequence. In this embodiment, channel
estimation is performed on all four symbols of the first length-4 OCC
sequence and all four symbols of the second length-4 OCC sequence to
support MIMO transmissions in a downlink channel.

[0009] In yet another embodiment, a method of communicating reference
signal symbols is provided. In this example, the method includes
communicating a first subframe carrying a first length-2 OCC sequence and
a second length-2 OCC sequence. The method further includes communicating
a second subframe carrying a third length-2 OCC sequence and fourth
length-2 OCC sequence. In this embodiment, channel estimation is
performed on all four length-2 OCC sequences to support MIMO
transmissions having five or more layers of spatial multiplexing in the
downlink channel.

[0010] In yet another embodiment, a method of communicating reference
signal symbols is provided. In this example, the method includes
communicating a first subframe comprising a first resource block pair
(RBP) that carries a first length-2 OCC sequence and a second length-2
OCC sequence both of which correspond to a first set of four antenna
ports. The first subframe further comprises a second RBP carrying a third
length-2 OCC sequence and a fourth length-2 OCC sequence both of which
correspond to a second set of four antenna ports that is different from
the first set of antenna ports. In this example, channel estimation is
performed on the first length-2 OCC sequence, the second length-2 OCC
sequence, the third length-2 OCC sequence, and the fourth length-2 OCC
sequence to support MIMO transmissions having five or more layers of
spatial multiplexing in the downlink channel.

[0011] Other embodiments of this disclosure include apparatuses/devices
for executing and/or facilitating the execution of one or multiple steps
of the methods summarized above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a more complete understanding of the present invention, and the
advantages thereof, reference is now made to the following descriptions
taken in conjunction with the accompanying drawing, in which:

[0014]FIG. 2 illustrates a diagram of a prior-art subframe for carrying
DM-RS symbols;

[0015]FIG. 3 illustrates a diagram of another prior-art subframe for
carrying DM-RS symbols;

[0016]FIG. 4 illustrates a diagram of an embodiment of a transmission
sequence for carrying DMRS symbols in two length-4 orthogonal cover codes
(OCCs);

[0017] FIG. 5 illustrates a diagram of an embodiment of a transmission
sequence for carrying DMRS symbols in four length-2 OCCs;

[0018] FIG. 6 illustrates a diagram of another embodiment of a
transmission sequence for carrying DMRS symbols in four length-2 OCCs;

[0019] FIG. 7 illustrates a diagram of an embodiment of a transmission
sequence for carrying DMRS symbols in two length-2 OCCs;

[0020]FIG. 8 illustrates a diagram of another embodiment of a
transmission sequence for carrying DMRS symbols in two length-4 OCCs;

[0021]FIG. 9 illustrates a diagram of another embodiment of a
transmission sequence for carrying DMRS symbols in four length-2 OCCs;
and

[0022] FIG. 10 illustrates a block diagram of an embodiment of a
communications device.

DETAILED DESCRIPTION

[0023] The operating of the current example embodiments and the structure
thereof are discussed in detail below. It should be appreciated, however,
that the present invention provides many applicable inventive concepts
that can be embodied in a wide variety of specific contexts. The specific
embodiments discussed are merely illustrative of specific structures of
the invention and ways to operate the invention, and do not limit the
scope of the invention.

[0024] Although aspects of this disclosure are discussed in the context of
LTE, they may generally be applied to other standards compliant
communications systems, such as Institute of Electrical and Electronics
Engineers (IEEE) 802.16, WiMAX, 3GPP2 systems, and the like.

[0025] One challenge in 3GPP LTE rel-10 is that the downlink subframe may
be incapable of carrying enough DM-RS symbols to support five or more
layers of spatial multiplexing when channel conditions are less than
ideal (e.g., when poor synchronization prevents transmitting one or more
timeslots of the subframe). Such may occur when attempting to transmit
data on the backhaul link of a relay node. As such, techniques for
transporting sufficient amounts of DM-RS signals during non-ideal channel
conditions (e.g., sub-optimal synchronization) are desired so that five
or more layers of spatial multiplexing (e.g., eight layers) may be
reliably supported.

[0026] FIG. 1 illustrates a diagram of a wireless communications network
100 for supporting communications that utilize eight-layer spatial
multiplexing MIMO transmission techniques. The wireless communications
network 100 may include an evolved NodeB (eNB) 105, a plurality of user
equipments (UEs) 110-120, and a relay node (RN) 125. The eNB 105 may be
any component or collection of components that is capable of
communicating with the one or more of the UEs 110-120 and/or RN 125, and
may be elsewhere referred to as a controller, a communications
controller, a base station, a NodeB, etc. The eNB 105 may communicate
with the UEs 110-120, the RN 125, and/or other nodes/devices (e.g.,
including those not explicitly depicted in FIG. 1), via one or more
downlink channels (e.g., PDSCH, PDCCH, etc.), as well as one or more
uplink channels (e.g., an uplink shared channel (UL-SCH), etc.). The UEs
110-120 may be any component or collection of components that allow a
user to access the wireless communications network 100, and may be
elsewhere referred to as mobiles, mobile stations, subscribers, users,
terminals, wireless nodes, etc. The RN 125 may be any component or
collection of components that facilitates a user's access to the wireless
communications network 100 by extending the range of an uplink or
downlink transmission. For instance, the RN 125 may serve as an
intermediary between the UE 120 and the eNB 105, thereby relaying
communications back and forth between the two parties.

[0027]FIG. 2 illustrates a diagram of a normal subframe 200 carrying a
standard DM-RS. As shown, the subframe 200 carries two length-4
orthogonal cover codes (OCCs) 201-202 in resource elements (REs) 222-245,
which are positioned in the T5, T6, T12, and T13 timeslots of the
subframe 200. The DM-RS symbols carried in the two length-4 OCCs 201-202
may be used for performing channel estimation in the PDSCH, and may
support five or more layers of spatial multiplexing (e.g., up to eight
layers of spatial multiplexing). A first instance of the length-4 OCC 201
may span four REs 222-223 and 234-235 positioned in a first subcarrier
(f1) of the subframe 200, while a first instance of the length-4 OCC
202 may span four REs 224-225 and 236-237 position in a second subcarrier
(f2) of the subframe 200. A second and third instance of the
length-4 OCC 201 may be repeated in a sixth subcarrier (f6) and an
eleventh subcarrier (f11), respectively, of the subframe 200, while
a second and third instance of the length-4 OCC 202 may be repeated in a
seventh subcarrier (f7) and an twelfth subcarrier (f12),
respectively, of the subframe 200. The second and third instances of the
length-4 OCCs 201-202 allow for accurate estimation of the channel (e.g.,
over various sub-channels).

[0028] In some situations, channel conditions and/or synchronization
problems may prevent the effective transmission of the last timeslot
(e.g., the T13 timeslot) of a subframe. FIG. 3 illustrates a diagram of a
subframe 300 carrying a standard DM-RS pattern in non-ideal channel
conditions. As shown, the 13 T timeslot of the subframe 300 is not
transmitted, and consequently is incapable of carrying the last DM-RS
symbol. Further, the T12 timeslot is prevented from carrying DM-RS by
virtue of the symbol loss in the T13 timeslot because DM-RS symbols are
carried in pairs of consecutive REs. Hence, the REs 334-337 remain empty,
thereby preventing the subframe 300 from carrying a length-4 OCC.
Instead, the subframe 300 is restricted to carrying two length-2 OCCs 301
and 302, a first instance of which is carried in the REs 322-323 and
324-325 (respectively), and a second and third instance of which are
carried in the f6-f7 and f11-f12 subcarriers. The
length-2 OCCs 301-302 are capable of supporting two antenna ports apiece,
and hence the subframe 300 can support a maximum of four layers of
spatial multiplexing (e.g., 5, 6, 7, or 8 antenna ports). Accordingly,
techniques for supporting more than four layers of spatial multiplexing
during non-ideal channel conditions are desired.

[0029] One solution to supporting eight layers of spatial multiplexing
during non-ideal channel conditions is to carry two length-4 OCCs using
two subframes. FIG. 4 illustrates a transmission sequence 400 for
carrying two length-4 OCCs 401-402 over a pair of subframes. As shown,
the first two symbols of each of the length-4 OCCs 401-402 are carried in
a first subframe (e.g., subframe n), while the second two symbols of each
of the length-4 OCCs 401-402 are carried in a subsequent subframe (e.g.,
subframe n+k). Specifically, the subframe n carries the first two symbols
of the length-4 OCC 401 in the REs 422-423 and the first two symbols of
the length-4 OCC 402 in the REs 424-425. The subframe n+k carries the
third and fourth symbols of the length-4 OCC 401 in the REs 472-473 and
the third and fourth symbols of the length-4 OCC 402 in the REs 474-475.
Second and third instances of the length-4 OCCs 401-402 are carried in
the f6-f7 and f11/f12 subcarriers of the subframe n
and the subframe n+k. Accordingly, the transmission sequence 400 supports
up to eight layers of spatial multiplexing even when the T13 timeslot of
one (or both) of the subframe n and the subframe n+k are unavailable for
carrying DM-RS symbols. Table 1 below shows possible bit sequences for
identifying antenna ports in the transmission sequence 400. The symbol
"O" indicates that no signal is transmitted.

[0030] As shown above in Table 1, the T4 and T5 timeslots of the subframe
n and the subframe n+k carry a DM-RS sequence capable of supporting eight
layers of spatial multiplexing. Notably, both the third and fourth
symbols of the DM-RS sequence are not carried in (omitted or otherwise
excluded from) the subframe n, while both the first and second symbols of
the DM-RS sequence are excluded/omitted from the subframe n+k. In other
words, neither the third nor the fourth symbols of the DM-RS sequence are
carried in the subframe n, while neither the first nor the second symbols
of the DM-RS sequence are carried in the subframe n+k.

[0031] Notably, the subframe n and subframe n+k may be consecutive frames
(e.g., k=|1|) or non-consecutive frames (e.g., k>|1|), and may be
transmitted in reverse order such that the subframe n is transported
through the downlink channel after the subframe n+k (e.g., k<0).
Because the position and sequencing of the subframe n and subframe n+k
may vary, a means for allowing the receiver (e.g., the UE or the RN) to
identify/locate the various subframe types (e.g., n_type and n+k_type
frames) may be needed or desired. There are various ways to facilitate
the location of subframe types by the receiver.

[0032] In one embodiment, the location of frame types may be accomplished
through an implicit assignment such that some subframes are always n_type
frames while other subframes are always n+k_type frames. A simple example
of implicit assignment may be that every even subframe carries an n_type
frame, while every odd subframe carries an n+k_type frame. Such an
implementation is purely exemplary, as other patterns of implicit
assignment may be used as well, e.g., patterns that allow less frequent
communication of n_type and n+k_type frames, such as every-other third
frame, etc.

[0033] In other embodiments, the location of frame types may be
accomplished through higher layer signaling, e.g., radio resource control
(RRC) signaling, Operation, Administration and Maintenance (OAM)
signaling, etc. For instance, the eNB may send a message that indicates
the location of an n_type frame and/or an n+k_type frame. In such
embodiments, a bitmap or bitmap field may be used that includes a
signaling bit for each subframe sent during a given period (e.g., 10
milliseconds (ms), . . . , 40 ms, etc.). The bitmap field may be similar
to that included in Multicast-Broadcast Single Frequency Network (MBSFN)
subframes. In some embodiments, the bitmap may include values for all
subframes, including those frames that are not assigned to the Un link or
the Uu link, in addition to Uu/Un link subframes. Alternatively, the
bitmap may only include values for frames assigned to the Un/Uu link,
which may advantageously achieve more compact signaling. One disadvantage
of the bitmap only including values for frames assigned to the Un/Uu link
is that more frequent bitmap transmissions may be required, as an updated
bitmap may be sent every time the Un/Uu subframe allocation is modified.

[0034] In yet other embodiments, the location of frame types may be
accomplished through Service Integration Bus (SIB) messaging. In such
embodiments, all recipients (e.g., all RNs/UEs being served by the eNB)
may identify subframe types according to a common pattern/scheme, e.g.,
as indicated by the SIB messaging. For instance, the position/sequence of
n_type and n+k frames may be the same for a first UE as a second UE.
Although the signaling may be simplified, such embodiments may lack the
flexibility of other techniques for locating frame types.

[0035] In yet other embodiment, the location of frame types may be
accomplished by predefining antenna ports. Such a configuration may be
implemented using RRC or OAM signaling, and may be facilitated by the
defining of new antenna ports in a relevant communications standard, such
as 3GP TS 36.2111.

[0036] In embodiments where the subframe n and subframe n+k are not
adjacent, it may be possible to specify (e.g., using a table) the
locations of subframe n+k in relation to subframe n. Table 2 illustrates
such a table, which is included for exemplary purposes as other
positional mappings may be used in various embodiments. Notably, when k
is a positive integer, the subframe n+k is transmitted after subframe n.
When k is a negative integer, subframe n+k is transmitted prior to
subframe n.

[0037] As an alternative to mapping the specific location of the two
subframes, a table with generic patterns may be used for building a
variety of possible Un subframe configurations. This may be done by
indicating the corresponding subframe n+k for each subframe n using an
index. In embodiments, the UL/DL configuration may be a combination of
one or several generic sub-patterns that is uniquely identified by a list
of indices. An exemplary table of the indices is depicted in tables 3 and
4. For instance, `Subframe Configuration Index #4` (in Table 2) may be
configured with index 5 and/or index 17 from Table 3. For instance
(according to Table 4), when index 8 is used, the 5th subframe
(e.g., S4) in a set may correspond to a subframe n type, and the
8th subframe (e.g., S4+3=S7) in the set may correspond to
a subframe n+k type.

[0038] An alternative solution for supporting eight layers of spatial
multiplexing during non-ideal channel conditions is to carry four
length-2 OCCs using two subframes. FIG. 5 illustrates a transmission
sequence 500 for carrying four length-2 OCCs 501-504 in a pair of
subframes. As shown, the length-2 OCCs 501-502 are carried in the
subframe n, while the length-2 OCCs 503-504 are carried in the subframe
n+k. Additional instances of the length-2 OCCs 501-504 are carried in the
f6-f7 and f11-f12 subcarriers of the subframe n and
the subframe n+k. The length-2 OCCs 501-502 may support a first set of
antenna ports (e.g., 7, 8, 9, 10), while the length-2 OCCs 503-504 may
support a second set of antenna ports (e.g., 11, 12, 13, 14).
Accordingly, the transmission sequence 500 supports up to eight layers of
spatial multiplexing even when the T13 timeslots of one (or both) of the
subframe n and the subframe n+k are unavailable for carrying DM-RS
symbols.

[0039] Yet another alternative solution for supporting eight layers of
spatial multiplexing during non-ideal channel conditions is to carry four
length-2 OCCs in different RBs (i.e., different frequency bands) of the
same subframe (e.g., using more frequency resources to carry DM-RS
symbols). Such a solution may be attractive when the channel coherence
bandwidth is relatively large. FIG. 6 illustrates a transmission sequence
600 for carrying two length-2 OCCs 601-602 in a first RB pair (RBPm)
of the subframe n and an additional two length-2 OCCs 603-604 in a second
RBP (RBPm+l) of the subframe n. Notably, the RBPm includes
subcarriers f1-f12 of the subframe n, while the RBPm+l
includes subcarriers fj-f.sub.(j+11). Additional instances of
length-2 OCCs 601-602 are carried in the f6-f7 and
f11-f12 subcarriers of the RBPm, while additional
instances of length-2 OCCs 603-604 are carried in the
f.sub.(j+5)-f.sub.(j+6) and f.sub.(j+5)-f.sub.(j+11) subcarriers of the
RBPm+l. In some embodiments, the length-2 OCCs 601-602 may support a
first set of antenna ports (e.g., 7, 8, 9, and 10), while the length-2
OCCs 603-604 may support a second set of antenna ports (e.g., 11, 12, 13,
14). Accordingly, the transmission sequence 600 supports up to eight
layers of spatial multiplexing even when the T13 timeslots of the
subframe n is unavailable for carrying DM-RS symbols.

[0040] When only four layers of spatial multiplexing are desired, a pair
of length-2 OCCs may be carried in different RBPs of the same subframe.
FIG. 7 illustrates a transmission sequence 700 for carrying a length-2
OCC 701 in a RBPm of the subframe n and a length-2 OCC 702 in a
RBPm+l of the subframe n. Additional instances of the length-2 OCC
701 are carried in the f6-f7 and f11-f12 subcarriers
of the RBPm, while additional instances of length-2 OCC 702 are
carried in the f.sub.(j+4)-f.sub.(j+5) and f.sub.(j+10)-f.sub.(j+11)
subcarriers of the RBPm+l. Each of the length-2 OCCs 701-702 may
support two antenna ports, thereby allowing the transmission sequence 700
to support up to four layers of spatial multiplexing (irrespective of
symbol loss in the T13 timeslot).

[0041] Yet another solution for supporting eight layers of spatial
multiplexing during non-ideal channel conditions is to carry two length-4
OCCs in non-adjacent RBPs of two subframes. FIG. 8 illustrates a
transmission sequence 800 for carrying a first length-4 OCC 801 a first
RBP of the subframe n and the subframe n+k, and a second length-4 OCC 802
in the RBPm+l of the subframe n and the subframe n+k. Specifically,
the first and second symbols of the length-4 OCC 801 are carried by the
RBPm of the subframe n, while the second and third symbols of the
length-4 OCC 801 are carried by the RBPm of the subframe n+k.
Likewise, the first and second symbols of the length-4 OCC 802 are
carried by the RBPm+l of the subframe n, while the third and fourth
symbols of the length-4 OCC 802 are carried by the RBPm+l of the
subframe n+k. In embodiments, the length-4 OCC 801 may support a first
set of antenna ports (e.g., 7, 8, 9, and 10), while the length-4 OCC 802
may support a second set of antenna ports (e.g., 11, 12, 13, and 14).
Hence, the sequence 800 may support up to eight layers of spatial
multiplexing even when the T13 timeslots of one (or both) of the subframe
n and the subframe n+k are unavailable for carrying DM-RS symbols.

[0042] Yet another solution for supporting eight layers of spatial
multiplexing during non-ideal channel conditions is to carry four
length-2 OCCs in non-adjacent RBPs of two subframes FIG. 9 illustrates a
transmission sequence 900 for carrying four length-2 OCCs 901-904. As
shown, the length-2 OCC 901 is carried by the RBPm of the subframe
n, the length-2 OCC 902 is carried by the RBPm+l of the subframe n,
the length-2 OCC 903 is carried by the RBPm of the subframe n+k, and
the length-2 OCC 904 is carried by the RBPm+l of the subframe n+k.
In embodiments, the length-2 OCC 901 may support a pair of antenna ports
(e.g., 7 and 8), the length-2 OCC 902 may support a pair of antenna ports
(e.g., 9 and 10), the length-2 OCC 903 may support a pair of antenna
ports (e.g., 11 and 12), and the length-2 OCC 904 may support a pair of
antenna ports (e.g., 13 and 14). Hence, the sequence 900 may support up
to eight layers of spatial multiplexing even when the T13 timeslots of
one (or both) of the subframe n and the subframe n+k are unavailable for
carrying DM-RS symbols.

[0043] FIG. 10 illustrates a block diagram of an embodiment of a base
station 1000. The base station 1000 may include a processor 1002, a
memory 1004, a cellular interface 1010, a transmitter array 1020, a
receiver array 1025, and an auxiliary interface 1030, which may (or may
not) be arranged as shown in FIG. 10. The processor 1002 may be any
component capable of performing computations and/or other processing
related tasks, and the memory 1004 may be any component capable of
storing programming and/or instructions for the processor 1002. The
cellular interface 1010 may be any component or collection of components
that allows the base station 1000 to communicate using a cellular signal,
and may be used to receive and/or transmit information over a cellular
connection of a cellular network. The transmitter array 1020 may be any
device that facilitates a wireless transmission by the base station 1000
via the cellular interface 1010. In an embodiment, the transmitter array
1020 may comprise a plurality of antennas (or antenna ports) that enable
the base station 1000 to implement MIMO techniques. In such embodiments,
the transmitter array 1020 may have as many as eight (or more)
antennas/antenna-ports for engaging in multi-layer (e.g., eight or more
layers) of spatial multiplexing. The receiver array 1025 may be any
device that facilitates reception of a wireless signal by the base
station 1000 via the cellular interface 1010. In an embodiment, the
receiver array 1025 may comprise a plurality of antennas (or antenna
ports) that enable the base station 1000 to implement MIMO techniques,
including, for example, multiuser and/or single user uplink MIMO
communication. The auxiliary interface 1030 may be any component or
collection of components that allows the base station 1000 to communicate
with other devices (e.g., backhaul networks, other base stations), and
may be used to implement either a wire-line or wireless connection with
the devices.

[0044] Notably, aspects of this disclosure may be applicable to
transmissions involving a reduced DM-RS sequence (e.g., as may
potentially be set-forth in future LTE releases) as well as transmissions
involving an extended cyclic prefix subframe (e.g., where four DM-RS
sequences are transmitted). These are mentioned herein for exemplary
purposes only, and represent only two of the numerous possible
implementations to which aspects of this disclosure may apply.

[0045] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing from
the spirit and scope of the invention as defined by the appended claims.
Accordingly, the appended claims are intended to include within their
scope such processes, machines, manufacture, compositions of matter,
means, methods, or steps.